1. Field of the Invention
The present invention relates to a surface acoustic wave device and, more particularly, a surface acoustic wave device such as a surface acoustic wave filter.
2. Description of the Related Art
Surface acoustic wave devices are used in antenna duplexers of mobile communications devices such as cellular phones. Miniaturization of mobile communication apparatuses and additional miniaturization of surface acoustic wave devices in keeping with the trend toward greater complexity are required.
In cases where a surface acoustic wave device is used in an antenna duplexer, a transmission surface acoustic wave (SAW) filter and a reception surface acoustic wave (SAW) filter are formed on the same common chip for the sake of miniaturization.
Here, cases arise where a signal that is inputted by a transmission terminal is converted into a surface acoustic wave by a transmission resonator and a short circuit is formed so that the surface acoustic wave is propagated and linked to the reception resonator. In such a case, the transmission/reception isolation characteristic deteriorates and the filter transmission characteristic is subject to spurious emission.
As conventional techniques for solving this problem, a technique that provides a groove by means of dicing between two SAW filters on a piezoelectric substrate (Japanese Patent Application Laid Open Nos. H5-102783 and 2000-13179), or a technique that allows one filter to carry parts that intersect lines that are connected to a signal terminal and lines that are connected to a ground terminal (Japanese Patent Application Laid Open No. 2003-51731), have been disclosed.
However, in the inventions appearing in Japanese Patent Application Laid Open Nos. H5-102783 and 2000-13179, the fine processing of the processing technology is problematic, there are resonator problems and limitations on placement, and there is the risk of an increase in chip size. In addition, deterioration in the characteristics is induced because chips fly toward the resonator when a groove is provided by means of dicing.
On the other hand, an object of the invention according to Japanese Patent Application Laid Open No. 2003-51731 is to prevent worsening of the isolation and the attenuation amount caused by reciprocal induction that is produced in order to counteract the magnetic flux that arises due to the influence of the current flowing to the filter.